Thermostatic switch with solid state heater

ABSTRACT

The switch has a base, a cover, and three, spaced terminals that are secured intermediate their ends in the base to extend at opposite ends beneath the base, and into the cover, respectively. An electrical heater element is secured at opposite ends to two of the terminals to extend therebetween within the cover. A bimetallic, temperature-responsive switch arm is secured at one end to a tab which projects laterally from one of said two terminals, and normally is releasably engaged at its opposite end with the third terminal. The switch arm can be calibrated after assembly electrically by adjusting the power supplied to the heater element, or mechanically by inserting an instrument through a hole in the base to bend said tab to increase or decrease the tension in said arm when closed.

United States Patent 11 1 1111 3,870,985 Hire Mar. 11, 1975 THERMOSTATIC SWITCH WITH SOLID 3,621,432 11/1971 Beck 337/377 x STATE HEATER Primary ExaminerArthur T. Grimley [75] Inventor: Charles John Hire, Pittsford, NY.

[73] Assignee: Fasco Industries, Inc., Rochester, [57] ABSTRACT The switch has a base, a cover, and three, spaced ter- [22] Wed: 1973 minals that are secured intermediate their ends in the 21 App| 402 15 base to extend at opposite'ends beneath the base, and

into the cover, respectively. An electrical heater element is secured at opposite ends to two of the termi- [52] US. Cl 337/381, 337/360, 337/377 nals to extend therebetween within the cover A [51] Int. Cl. H0lh 37/04, HOlh 37/12 metallic temperature responsive switch arm is [58] held of Search 337/37 1021 cured at one end to a tab which projects laterally from 337/349 112; 323/68 one of said two terminals, and normally is releasably engaged at its opposite end with the third terminal. [56] References cued The switch arm can be calibrated after assembly elec- UNITED STATES PATENTS trically by adjusting the power supplied to the heater 2,945,833 7/1960 Girolamo etal 337/113x element, or mechanically y inserting an instrument 3,248,501 4/1966 Hire 337/37 through a hole in the base to bend said tab to increase 3,267,237 8/1966 Gelzer 337/113 X or decrease the tension in said arm when closed. 3,526,753 9/1970 Aisanich et al. 323/68 x 3,546,651 12/1970 Moorhead et al. 337/113 x; 10 Claims, 7 Drawing Figures i 43 IL I I 32- Z7 24 41 25 7* 38 44 i 1 1 I i I 1 l i l l I4 I d R M VOLTAGE SOURCE PATENTEU W1 1 I975 sum 1 or z VOLTAGE SOURCE FIG. 3

PATENTEB MARI 1 I975 SHEET 2 BF 2 FIG. 5 o 3? w 35, 32L! 7H 62 K35 3 so! D u a FIG. 6 62 52 \Z ee 53 3f IZJ 3 FIG. 7

THERMOSTATIC SWITCH WITH SOLID STATE HEATER This invention relates to thermostatic switches, and more particularly to an improved thermostatic switch of the type containing a resistance element for preheating the switch to adjust its opening or closing time.

Thermostatic switches of the type which incorporate a resistance element for selectively preheating the temperatureresponsive actuator in the switch to calibrate or otherwise vary its operating range are well known. (See for example my U.S. Pat. No. 3,248,501.) A major disadvantage of prior such switches, however, is that they have been relatively expensive to manufacture, and difficult to calibrate with any great degree of accuracy. t

It is an object of this invention, therefore, to provide an improved thermostatic switch of the type containing an electrical heating element for adjustably setting the operating range of the switch.

Another object of this invention is to provide an improved thermostat of the preheatable variety, which can be readily adjusted mechanically and/or electrically to vary its switch opening or closing times.

Still another object of this invention is to provide an improved, preheatable thermostat of the type having a cantilevered, bi-metallic switch arm, which can be readily calibrated after assembly of the switch.

These and other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.

In the drawings:

FIG. 1 is a side elevational view of a thermostatic switch made according to one embodiment of this invention, with portions of its base and cover being broken away and shown in section, and illustrating schematically one manner in which this switch may be wired in a circuit;

FIG. 2 is a plan view of this switch with its cover removed;

FIG. 3 is an end elevational view of this switch as seen when looking toward its right end as shown in FIG. 1, and with its cover removed;

FIG. 4 is a schematic wiring diagram illustrating still another way this switch may be used;

FIG. 5 is a side elevational view of a modified form of this switch with portions of its base and cover broken away and shown in section;

FIG. 6 is a plan view of this modified switch with its cover removed, and with portions of its heating element cut away; and

FIG. 7 is an end elevational view thereof as seen from the right end of this switch as shown in FIG. 5, and again with its cover removed.

Referring now to the drawings by numerals of reference, and first to the embodiment illustrated in FIGS. 1 to 3, 10 denotes generally a thermostatic switch comprising an elongate, generally flat base section 12, which may be made from any known, rigid dielectric material. Adjacent its lower end section 12 is surrounded by a narrow, integral flange 13, portions of which are notched out as at 14 on opposite sides of the thermostat for mounting purposes. The upper end of base 12, the portion above its flange 13, projects snugly and part way into the lower end of an inverted, hollow cover section 15 (FIG. 1), which is secured at its open end around the base 12 and against its flange 13.

Secured intermediate their ends in the base 12 adjacent opposite ends thereof, and projecting above and below the base in spaced, parallel planes, are two metal plates or terminals 20 and 21. A third metal terminal 22, which is secured intermediate its ends in the base 12 centrally thereof, also projects at its lower end beneath the base, but has its upper end bent laterally as at 24 to seat horizontally in an elongate groove or recess 25 that is formed in the upper surface of the base medially ofits sides. Each of the two outer terminals 20 and 21, on the other hand, projects into cover 15 above base 12 and has therein adjacent its upper end a small rectangular opening 26 (FIG. 3). A small tang 27, which is struck from each terminal 20 and 21 projects slightly above and outwardly of the lower edge of each opening 26 centrally thereof.

Extending transversely between terminals 20 and 21, and with opposite ends thereof seated on the lower edges of openings 26 in abutment with the tangs 27, is a ceramic backing plate 31. Mounted on the upper surface of plate 31, and substantially coextensive therewith, is a conventional, solid state heater element 35 of the planar, electrical resistance variety. Plate 31 and the heater element 35 are fastened to terminals 20 and 21 by conventional, generally U-shaped spring clips 32 and 33. The two legs of each clip 32, 33 extend into an opening 26 from the inside of the associated terminal 20, 21 so that the lower legs (FIG. 1) of the clips resiliently engage opposite ends of element 35, and so that lips 32 and 33' on the upper legs of clips 32 and 33, respectively, engage resiliently over the upper, outer edges ofthe openings 26. The metal spring clips 32 and 33 function also to connect opposite ends of element 35 electrically to terminals 20 and 21.

The exact manner in which the heater element 35 is applied on the ceramic backing plate 31 forms no part of this invention, and therefore is not described in detail herein.

Between the base 12 and the ceramic backing member or plate 31 terminal 21 has thereon a laterallyprojecting tang or tab 38, which is struck from an opening 39 in the terminal to project at right angles therefrom into the recess 25. The inner or free end of the tab 38 registers with a vertical opening 39 that is formed in the base section 12 adjacent terminal 21. A pivotal, bimetallic switch arm 41 is spot welded or otherwise secured at one end (its right end in FIG. 1) to the inner end of the tab 38 so that the low expansive side thereof faces upwardly in FIG. 1. Arm 41 projects horizontally into the space between base 12 and the backing member 31 so that its free end overlies the upper end 24 of the terminal 22. An annular magnet 44 is secured by a metal rivet 43 to the free end of arm 41 normally to attract the arm into its closed position (FIG. 1) wherein the lower end of rivet 43 is held in contact with the upper end 24 of the terminal 22, thereby normally to connect terminals 21 and 22 electrically to one another.

When used as shown in FIG. 1, the motor M or a timer or the like may be connected between terminals 21 and 22 to be controlled by the contacts 24, 43. Also, the heater element 35 may be connected at one end through contacts 24, 43 and by terminal 22 to one side of a voltage source (FIG. 1), and its other end through terminal 20 and an adjustable resistor R to the opposite side of the voltage source. With this construction power is supplied to the heater element 35 through the adjustable resistor R, so that the amount of power applied to element 35, and hence the heat emitted thereby, can be controlled by adjusting the resistor R. The heat generated by element 35 increases the ambient temperature within switch 10, so that a correspondingly smaller increase in the ambient temperature at the outside of the switch will be required to open switch arm 41 as compared, for example, to the increase in the external ambient temperature that would be required if the heater element 35 were not employed to preheat the bi-metallic arm 41.

Still another way of adjusting the operating temperature of the thermostat is to adjust the position of the tab 38 mechanically. This can be done by inserting a tool through the opening 39 in the base 12 either to bend the tab 38 upwardly to increase the tension in the arm 41, and thus to cause it to open at a lower ambient temperature, or to bend the tab 38 downwardly to decrease the aforementioned tension in the arm 41 so that the switch will tend to remain closed until higher ambient temperatures are reached.

lt'will be seen, therefore, that the operating range of the switch arm will depend upon the amount of resistance that is introduced into the circuit by the resistor R, the inherent resistance of the heating element 35 itself, and the mechanical positioning of the calibrating tab 38. The resistor R and the tab 38, of course, provide ready means for adjusting within limits, the operating range of the thermostat 10. The advantage of using the tab 38 for calibrating the switch is that the calibration does not have to be made until after the entire switch has been assembled, so that the contents of the switch will not be subjected to stray air currents, which would adversely affect its calibration, if this operation were to be performed, say, while the cover 15 was off.

As shown in FIG. 4, the motor M could, if desired, be connected in parallel with element 35 between terminals 20 and 21. Line voltage could then be applied at one side to terminal 20 and at its opposite side through an extender switch S to terminal 22. This provides novel means for extending the cycle times used in dishwashers, home laundry equipment, etc.

Referring now to FIGS. 5 to 7', wherein like numerals are employed to denote elements similar to those employed in the first embodiment, 50 denotes generally a modified switch having a dielectric base section 12 and a cover 15. Two metal terminals 52 and 53, which are generally similar to terminals 20 and 21 in the first embodiment, are secured intermediate their ends in the base section 12 to project at the lower ends beneath the base, and at their upper ends into the cover adjacent opposite ends thereof. A third terminal 54, which is substantially similar to terminal 22 of the first embodiment, is secured in base 12 so that its upper, laterally off-set end55 overlies the upper surface of the base section 12 near its midpoint.

The portions of terminals 52 and 53, which project into cover 15 are laterally offset to one side. A ceramic backing plate 31 and its heater element 35 are secured by spring clips 32 and 33 in openings 26 in the upper ends of these two outer terminals to extend horizontally therebetween. and in slightly laterally offset relation to the centerline of the thermostat (FIGS. 6 and 7).

One leg of a right angular steel bracket 60 is secured to the inner side of the terminal 52 within the cover 15 so that the other leg of the bracket projects horizontally above the base 12 and in registry with an aperture 61 in the base. As shown in FIG. 6, the bracket 60 is located adjacent one side of cover 15, while the heater element 35 and its backing plate 31 are located adjacent the opposite side of the cover. One end of one leg 62 of a generally U-shaped bi-metallic switch arm 63 is lap welded or otherwise fastened to the top of the horizontally projecting leg of the bracket 60 so that arm 63 is cantilevered from the bracket 60. The other leg 64 of the switch arm is supported beneath and parallel to the heater element 35. A lateral projection 65 on the free end of leg 64 has an annular magnet 66 secured to the underside thereof by a rivet 67.

As in the first embodiment, the magnet 66 tends to hold the lower end of the rivet 67 in electrical contact with the upper end 55 of the terminal 54, so that terminals 52 and 54 normally are electrically connected to each other through the normally-closed contacts 55 and 67. When, however, the ambient temperature of switch 50 rises above a predetermined value, the bimetallic arm 63 will tend to flex its free end upwardly to disengage contact 67 from the upper end of terminal 54 thereby to open the circuit between this terminal and terminal 52.

Switch 50 may be utilized in a manner similar to that described above in connection with switch 10. For example, to adjust the opening time of contacts 55, 67 a variable resistor (not illustrated) may be connected, as in the first embodiment, in series with element 35 of switch 50. Moreover, the switch arm 63 can be calibrated mechanically by inserting a tool through the opening 61 in the base 12 to engage and bend the leg of bracket 60 to which the switch 63 is attached, so that, as in the first embodiment. the switch arm 63 can be prestressed, as desired, to adjust the temperature range required to open and close the arm.

From the foregoing it will be apparent that the instant invention provides an improved, readily adjustable thermostat of the preheat variety, which is substantially simpler in construction, and more readily adjustable than prior such thermostats. These new switches have thev means to adjust their opening times or operating ranges not only by adjustment of the variable resistance, which can be connected in circuit with their heater elements, but also they can be calibrated merely by bending their associated mounting tab 38 orbracket 60. The advantage of calibrating in this manner is that it can be done while the cover 15 is secured over the base section 12 of the switch so that a more accurate adjustment can be made because the contents of the switch is not subject to stray air currents, and the like, which would otherwise tend to vary the ambient temperature of the switch at the time it is being calibrated. It has been found that such thermostats will hold their calibrations through a wide range of ambient temperatures thus making the switches suitable for use as, for example, fast-acting thermoswitches or relays, slowacting time-delay thermoswitches, and adjustable slow or fast-action switches or time delays. Moreover since the operating ranges of these switches are readily adjustable, they can be used, for example, as novel means for extending the cycle timers used on dishwashers, home laundry equipment and similar devices.

Although in the embodiments illustrated herein the heater elements 35 have been shown secured to the upper sides of the ceramic backing members 31, it will be apparent that, if desired, the heater elements, properly insulated, could be applied to the under sides or surfaces of these elements (i.e., the sides facing the movable switch arms 41 and 63). Preferably, in the illustrated embodiments, backing member 31 is made from a dielectric material which conducts heat very readily, so that any heat generated by a heater element positioned on top of the backing member 31 will be rapidly conducted through member 31 toward the switch arm.

Thus having described my invention, what I claim is: l. A thermostatic switch, comprising a housing having therein a chamber and a hole connecting the chamber to the exterior of the housing,

three spaced electrically conductive terminals secured to said housing, each having its opposite ends, respectively, projecting into said housing and extending exteriorly of said housing,

an electrically operable heater element mounted in said chamber and connected at opposite ends to two of said terminals,

a metal tab secured to and projecting from one of said two terminals and registering with said hole, a flexible, bi-metallic switch arm mounted in said housing adjacent said heater element and having a free end overlying the third of said three terminals,

an electrical contact secured on said free end of said arm, and

means securing the opposite end of said arm to said tab for pivotal movement, upon predetermined changes in its ambient temperature, between a position in which the contact on the free end of said arm is in engagement with said third terminal and a position in which said contact is disengaged from said third terminal,

said tab being bendable manually by an instrument insertable through said hole in said housing to vary the tension in said arm. 1 2. A thermostatic switch as defined in claim 1, wherein said two terminals project at their inner ends into said chamber in spaced, parallel relation,

said heater element extends transversely between said inner ends of said two terminals adjacent one side of said chamber,

said remaining terminal has its inner end located adjacent the opposite side of said chamber in spaced relation to said heater element, and

said free end of said arm is pivotal in the space between said element and said inner end of said remaining terminal.

3. A thermostatic switch as defined in claim 2, including a magnet mounted on said free end of said switch arm and operative to resist movement of said contact from its closed to its open position.

4. A thermostatic switch as defined in claim 2, wherein said tab is struck from said one terminal to project into said chamber between said heater element and said opening, and

said one end of said arm is fastened to said tab adjacent the end thereof that is integral with said one terminal.

5. A thermostatic switch as defined in claim 2, wherein said tab projects from said one terminal at a point offset from said heater element,

said switch arm is generally U-shaped in configuration and has one leg thereof secured to said tab and the opposite leg thereof extending between said heater element and said inner end of said third terminal.

6. In combination with a thermostatic switch as defined in claim 11, a power supply and a variable resistance connected in series with said heater element through a pair of said terminals, whereby said switch may be calibrated selectively by varying said resistance and by bending said tab.

7. A thermostat switch, comprising a housing having therein a chamber,

three spaced electrically-conductive terminals secured to said housing, and each having its opposite ends projecting, respectively, into said chamber and exteriorly of said housing,

an electrically operable heater element secured at opposite ends thereof in said chamber to the inner ends of two of said terminals and extending transversely therebetween in spaced relation to the inner end of the third terminal,

a flexible, bi-metallic switch arm secured at one end to one of said two terminals and having its opposite, free end extending into the space between said heater element and said inner end of said third terminal,

an electrical contact secured to said free end of said switch arm and registering with said inner end of said third terminal for selective engagement therewith upon predetermined changes in the ambient temperature about said arm, and

means for adjusting the resilient force statically exerted on said free end of said arm when said contact is engaged with said inner end of said third terminal.

8. In combination with a thermostatic switch as defined in claim 7, means for applying an adjustable voltage drop across opposite ends of said heater element adjustably to elevate the ambient temperature about said arm by the heat emitted by said element.

9. A thermostatic switch as defined in claim 7, wherein said adjusting means comprises means in said housing operable manually from the exterior of said housing to bend said free end of said arm relative to said one terminal.

10 A thermostatic switch as defined in claim 7, including a pair of spring clips securing opposite ends of said heater element to said two terminals electrically to connect said opposite ends thereof to said two termi- 

1. A thermostatic switch, comprising a housing having therein a chamber and a hole connecting the chamber to the exterior of the housing, three spaced electrically conductive terminals secured to said housing, each having its opposite Ends, respectively, projecting into said housing and extending exteriorly of said housing, an electrically operable heater element mounted in said chamber and connected at opposite ends to two of said terminals, a metal tab secured to and projecting from one of said two terminals and registering with said hole, a flexible, bi-metallic switch arm mounted in said housing adjacent said heater element and having a free end overlying the third of said three terminals, an electrical contact secured on said free end of said arm, and means securing the opposite end of said arm to said tab for pivotal movement, upon predetermined changes in its ambient temperature, between a position in which the contact on the free end of said arm is in engagement with said third terminal and a position in which said contact is disengaged from said third terminal, said tab being bendable manually by an instrument insertable through said hole in said housing to vary the tension in said arm.
 1. A thermostatic switch, comprising a housing having therein a chamber and a hole connecting the chamber to the exterior of the housing, three spaced electrically conductive terminals secured to said housing, each having its opposite Ends, respectively, projecting into said housing and extending exteriorly of said housing, an electrically operable heater element mounted in said chamber and connected at opposite ends to two of said terminals, a metal tab secured to and projecting from one of said two terminals and registering with said hole, a flexible, bi-metallic switch arm mounted in said housing adjacent said heater element and having a free end overlying the third of said three terminals, an electrical contact secured on said free end of said arm, and means securing the opposite end of said arm to said tab for pivotal movement, upon predetermined changes in its ambient temperature, between a position in which the contact on the free end of said arm is in engagement with said third terminal and a position in which said contact is disengaged from said third terminal, said tab being bendable manually by an instrument insertable through said hole in said housing to vary the tension in said arm.
 2. A thermostatic switch as defined in claim 1, wherein said two terminals project at their inner ends into said chamber in spaced, parallel relation, said heater element extends transversely between said inner ends of said two terminals adjacent one side of said chamber, said remaining terminal has its inner end located adjacent the opposite side of said chamber in spaced relation to said heater element, and said free end of said arm is pivotal in the space between said element and said inner end of said remaining terminal.
 3. A thermostatic switch as defined in claim 2, including a magnet mounted on said free end of said switch arm and operative to resist movement of said contact from its closed to its open position.
 4. A thermostatic switch as defined in claim 2, wherein said tab is struck from said one terminal to project into said chamber between said heater element and said opening, and said one end of said arm is fastened to said tab adjacent the end thereof that is integral with said one terminal.
 5. A thermostatic switch as defined in claim 2, wherein said tab projects from said one terminal at a point offset from said heater element, said switch arm is generally U-shaped in configuration and has one leg thereof secured to said tab and the opposite leg thereof extending between said heater element and said inner end of said third terminal.
 6. In combination with a thermostatic switch as defined in claim 11, a power supply and a variable resistance connected in series with said heater element through a pair of said terminals, whereby said switch may be calibrated selectively by varying said resistance and by bending said tab.
 7. A thermostat switch, comprising a housing having therein a chamber, three spaced electrically-conductive terminals secured to said housing, and each having its opposite ends projecting, respectively, into said chamber and exteriorly of said housing, an electrically operable heater element secured at opposite ends thereof in said chamber to the inner ends of two of said terminals and extending transversely therebetween in spaced relation to the inner end of the third terminal, a flexible, bi-metallic switch arm secured at one end to one of said two terminals and having its opposite, free end extending into the space between said heater element and said inner end of said third terminal, an electrical contact secured to said free end of said switch arm and registering with said inner end of said third terminal for selective engagement therewith upon predetermined changes in the ambient temperature about said arm, and means for adjusting the resilient force statically exerted on said free end of said arm when said contact is engaged with said inner end of said third terminal.
 8. In combination with a thermostatic switch as defined in claim 7, means for applying an adjustable voltage drop across opposite ends of said heater element adjustably to elevate the ambient Temperature about said arm by the heat emitted by said element.
 9. A thermostatic switch as defined in claim 7, wherein said adjusting means comprises means in said housing operable manually from the exterior of said housing to bend said free end of said arm relative to said one terminal. 